In comparison to a thin film transistor liquid crystal display (TFT-LCD) serving as a mainstream display technology at present, an organic light emitting diode (OLED) display has advantages of wide angle of view, high brightness, high contrast ratio, low energy consumption, lightness, thinness and the like, and thus becomes a focus of the present flat panel display technology.
The driving methods for organic light emitting diode displays are classified into two categories: a passive matrix (PM) type and an active matrix (AM) type. In comparison to the passive matrix type driving, the active matrix type diving has advantages of large amount of displayed information, low power consumption, long service life of devices, high contrast ratio of pictures and the like. An equivalent circuit of the basic principle of a driving circuit of pixel unit for an active matrix type organic light emitting diode display in the prior art is as shown in FIG. 1, comprising: a switch transistor M1, a driving transistor M2, a storage capacitor C1 and an organic electroluminescent device D1. The drain of the switch transistor M1 is connected to the gate of the driving transistor M2. The gate of the driving transistor M2 is also connected to one end of the storage capacitor C1, the source thereof is connected to the other end of the storage capacitor C1, and the drain thereof is connected to the luminescent device D1. When the gate of the switch transistor M1 is strobed by a scanning signal Vscan(n), the switch transistor M1 is turned on to import a data signal Vdata from the source thereof. The driving transistor M2 generally works in a saturation area. The gate-source voltage Vgs,DTFT of the driving transistor M2 determines the magnitude of the current flowing through the driving transistor M2, so that the stable current is provided for the luminescent device D1. Vgs,DTFT=VDD-Vdata (where the driving transistor M2 is a P type transistor), and the VDD is a voltage-stabilization or current-stabilization driving voltage connected to the driving transistor M2 for providing the energy required for the luminescence of the OLED device D1. The storage capacitor C1 functions as keeping the gate voltage of the driving transistor M2 stable within one frame.
The inventor has found at least the following problems in the prior art: the current actually flowing through the OLED device is:
                              I          OLED                =                ⁢                              1            2                    ⁢          μ          ⁢                                          ⁢                      Cox            ⁡                          (                              W                /                L                            )                                ⁢                                    (                                                                                      Vgs                    ⁢                                          ,                      DTFT                                                                                        -                                                    Vth                                                              )                        2                                                  =                ⁢                              1            2                    ⁢          μ          ⁢                                          ⁢                      Cox            ⁡                          (                              W                /                L                            )                                ⁢                                                    (                                  Vdd                  -                                      V                    IRdrop                                    -                  Vdata                  -                  Vth                                )                            2                        .                              
Since the IR drop on a power supply signal line between the driving voltage VDD and the GND (the power supply signal line itself has a resistance, so there is a voltage drop, i.e., an IR drop, on the power supply signal line), the current provided to the OLED device will be influenced by the IR drop, so that an operating point achieving white balance will drift, and the change in the current will influence the distribution of the driving voltage VDD and the magnitude of the IR drop again. Accordingly, a dynamic interaction process is formed, and the problem of non-uniform display is caused.